/*
 * Copyright 2014 Google Inc. All Rights Reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.errorprone.bugpatterns;

import static com.google.errorprone.BugPattern.Category.JDK;
import static com.google.errorprone.BugPattern.MaturityLevel.EXPERIMENTAL;
import static com.google.errorprone.BugPattern.SeverityLevel.WARNING;
import static com.google.errorprone.matchers.Description.NO_MATCH;

import com.google.errorprone.BugPattern;
import com.google.errorprone.VisitorState;
import com.google.errorprone.bugpatterns.BugChecker.MethodInvocationTreeMatcher;
import com.google.errorprone.matchers.Description;
import com.google.errorprone.matchers.Matcher;
import com.google.errorprone.util.ASTHelpers;

import com.sun.source.tree.MethodInvocationTree;
import com.sun.tools.javac.code.Symbol;
import com.sun.tools.javac.code.Symbol.MethodSymbol;
import com.sun.tools.javac.code.Symbol.VarSymbol;
import com.sun.tools.javac.code.Type;
import com.sun.tools.javac.code.Type.ArrayType;
import com.sun.tools.javac.code.Types;
import com.sun.tools.javac.tree.JCTree.JCExpression;
import com.sun.tools.javac.tree.JCTree.JCMethodInvocation;
import com.sun.tools.javac.util.List;

/**
 * @author eaftan@google.com (Eddie Aftandilian)
 */
@BugPattern(name = "PrimitiveArrayPassedToVarargsMethod",
    summary = "Passing a primitive array to a varargs method is usually wrong",
    explanation = "When you pass a primitive array as the only argument to a varargs method, the "
        + "primitive array is autoboxed into a single-element Object array. This is usually "
        + "not what was intended.",
    category = JDK, severity = WARNING, maturity = EXPERIMENTAL)
public class PrimitiveArrayPassedToVarargsMethod extends BugChecker
    implements MethodInvocationTreeMatcher {

  /**
   * Assuming the argument in the varargs position is a single one of type int[], here is the
   * truth table:
   *     Param type    Should return     Why
   *     int...        false             Exact type match
   *     int[]...      false             Exact type match for the array element type
   *     T...          true              Will cause boxing
   *     Object...     true              Will cause boxing
   */
  private static final Matcher<MethodInvocationTree> isVarargs =
      new Matcher<MethodInvocationTree>() {
    @Override
    public boolean matches(MethodInvocationTree t, VisitorState state) {
      Symbol symbol = ASTHelpers.getSymbol(t);
      if (!(symbol instanceof MethodSymbol)) {
        return false;
      }
      MethodSymbol methodSymbol = (MethodSymbol) symbol;

      // Bail out quickly if the method is not varargs
      if (!methodSymbol.isVarArgs()) {
        return false;
      }

      // Last param must be varags
      List<VarSymbol> params = methodSymbol.getParameters();
      int varargsPosition = params.length() - 1;
      ArrayType varargsParamType = (ArrayType) params.last().type;

      // Is the argument at the varargsPosition the only varargs argument and a primitive array?
      JCMethodInvocation methodInvocation = (JCMethodInvocation) t;
      List<JCExpression> arguments = methodInvocation.getArguments();
      Types types = state.getTypes();
      if (arguments.size() != params.length()) {
        return false;
      }
      Type varargsArgumentType = arguments.get(varargsPosition).type;
      if (!types.isArray(varargsArgumentType)
          || !types.elemtype(varargsArgumentType).isPrimitive()) {
        return false;
      }

      // Do the param and argument types actually match? i.e. can boxing even happen?
      return !(types.isSameType(varargsParamType, varargsArgumentType)
          || types.isSameType(varargsParamType.getComponentType(), varargsArgumentType));

    }
  };

  @Override
  public Description matchMethodInvocation(MethodInvocationTree t, VisitorState state) {
    return isVarargs.matches(t, state) ? describeMatch(t) : NO_MATCH;
  }
}
